Carrier signaling system



Dec. 27, 1927. 1,654,080

R. A. HEISING CARRIER SIGNALING SYSTEM Filed Nov. 4. 1924 H 3 74DETFCTOR Ab iPLlFlER oscxtLAToR lm emor: Raymond A. Hal's/77g.

Patented Dec. 2?, 192? RAYMOND A. HEISING, F MTLLBUBN, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCOBFDRATED, OF NEW YORK, N. Y.,'ACORPORATION OF NEW YORK.

CARRIER SIGNALING SYSTEM.

Application filed November 4, 1924. Serial No. 747,732.

This invention relates to carrier signaling systems and moreparticularly to a method of and means for the secret transmission ofsignals between stations.

5 One oh'ect of this invention is to provide a signaling system whereinthe transmitted signals may be received onlyby certain authorizedstations.

Another object is to provide a secret signaling system wherein a minimumof power is used in long distance transmission.

These objects are accomplished by employing a system of transmissionwherein a carrier wave is modulated by signal currents,

1 the unmodulated carrier component is suppressed and the modulatedcomponents consisting of the side bands, one of which is renderedincapableof intelligible reception as by.

means of masking frequencies, are transmitted. The side band is maskedby superimposing upon it a side band resulting from modulating a carrierwave by delayed signal currents derived from the original modulatingsource. To produce the masking side band, energy of the signal currentsis stored and, after a definite time interval, is supplied together witha carrier wave to an auxiliary modulator in which they are combined. Thesignal is made intelligible at a receivin station by suppressing themasked side and and combining a wave of carrier frequency with theundistorted incoming wave component.

The invention will be hereafter described as applied to a radio system,but it is to be understood that this invention may beused in a carriersystem employing a line for guiding the waves.

The novel features which are believed to 40 be characteristic of thisinvention will be pointed out with particularity in the claims appendedhereto. The invention itself, however, as to itsobjects and advantages,the details of its organization and its mode of operation will be betterunderstood by referring to the following description taken in connectionwith the accompanying drawing in which:

Fig. 1 illustrates a transmitting system embodyin this invention;

Fig. 2 s owe a series of curves to be used in explaining the operationof the system shown in Fig. 1; and

Fig. 3 is a schematic representation of a system' adapted to receivewaves transmitted by the apparatus shown in Fig. 1.

Referring now to Fig. 1 there is shown a balanced modulator A which maybe of any type adapted to produce both side bands and suppress theunmodulated component of carrier frequency. A suitable system which maybe used for this purpose is shown and described in U. S. Patent1,343,307, June 15, 1920, to Carson. A wave of carrier frequencysupplied by an oscillator B is impressed upon the common input circuitofthe modulator A by means of coil 1. Speech currents produced in themicrophone circuit 3 are impressed upon the filament-grid circuit of themodulator A through transformer 4. The oscillator B is of any typeadapted to produce radio frequency oscillations. A suitable system whichmay be employed for this pur-' pose, if desired, .is shown and describedin detail in U. S. Patent 1,356,763, October 26, 1920, to Hartley.

In double side band transmission it is impossible to intelligiblyreceive signals unless the supplied carrier is of the exact frequencyand phase of the suppressed carrier. If one side band is suppressed,however, the supplied carrier may vary considerably and still produceintelligible signals. By transmitting a portion of the second side bandthis feature is taken advantage of and the difficulty of reception isincreased.

To assist in preventing an unauthorized station from being able tointelligibly receive the message being transmitted a carrier waveofconstantly varying frequency should preferably be used. For thispurpose a variable auxiliary condenser 10 of small capacity, included inthe fre uency determining circuit of the oscillator has its movableelement continuously driven by a motor 11.

The modulation products resulting from the operation of the modulator A,consisting solely of the modulated components of the carrier wave, i.e., both side bands, are impressed upon filter F, which is designed tosuppress a portion of one of the side bands and transmit only theremainder of this side band and all of the other side hand. Thesetransmitted side bands are represented by the curves a in Fig. 2. Theportion trans.- mitted through filter F, is the portion betweenpoints 1and 2. This is impressed uponthe input circuit of an amplifier E, whichmay consist of any number of stages.

Signals from source "3 are also supplied to the electromagnet 6 whichacts upon a telegraphone disc 7 operated by motor 8 to producevariations in the magnetic properties of the disc. These magneticvariations induce corresponding current variations in an electromagnet 9which is in spaced relation to electromagnet 6. The current variationsproduced in the magnet 9 will have a time lag depending upon the spacingof the two elctromagnets and the speed of rotation of the disc. Delayedsignal currents from electromagnet 9 are impressed upon balancedmodulator 0, upon which a carrier Wave is impressed by oscillator D.Oscillator D and mo-dulatorG operatein the same manner as thearrangement described above comprising the modulator A and oscillator B,to produce side band components only. These side bands will behereinafter termed the delayed side bands. A

.The frequency of oscillator D may be the same as that of oscillator Bor it may vary therefrom by or 100 cycles. If the frequency is taken sothat the upper side band from modulator G is superimposed on the such asthatrepresented by curve 1) between the points 1 and 3 of Fig. 2. Thisdelayed side band is impressed upon the input circuit of the amplifier Eand superimposed upon the side bands transmitted through the filter FThe superposed side bands consisting of those transmitted through thefilter F one of which is masked by the delayed side bandpassed by thefilter F and the other of which comprises the undisturbed side bandcomponent, after being amplified by the amplifier E, are supplied to andradiatedfrom the antenna 12.

Filters F, and F are band pass filters of anysuitable type, such as, forexample, those disclosed in U. S. Patent 1,227,114, May '22, 1917 toCampbelL- Figure 3 shows an arrangement adapted to receive the wavestransmitted by the system shown in Figure 1.

The waves radiated from the antenna 12 are received by the antennacircuit 13. The received waves are impressed upon a band pass filter E,which is designed to suppress the masked side band component and transmit only the undisturbed side band component, corresponding to theportion represented by curve a, between points 3 and 2 in Fig. 2. Theundisturbed side band component is supplied t a detector 15. Anoscillator 16- supplies 0 cillations of" carrier wave frequency to thisdetector in which they are continuously supplied noise currents are usedto modulate the carrier wave with the result that an operator afterlistening in for a period of time and becoming accustomed to thedisturbing noises may be, able to disregard them and hence distinguishthe desired signal from the disturbances.

In the present system, however, the disturbing noises occur only duringthe signaling intervals, they are of substantially the same pitch as thesignals, and hence are much more effective in masking the signal than inthe systems referred to above.

If in an unauthorized receiving station a local oscillator is. usedwhich supplies oscillations of exactly the same frequency as thesuppressed carrier it would be possible to receive the incoming signalsmore or less intelligibly without suppressing the masked side band.However, by slightly varying the frequency of the carrier supplied atthe transmission station it will be impossible foran unauthorizedreceiving station to reproduce the suppressed carrier with the resultthat the signal will be unintelligible unless the masked side band issuppressed.

If desired, the oscillator D may also have its frequency varied slightlyin a manner similar to that described above With reference to oscillatorB, to further increase the difliculty of reception.

In secrecy transmission systems it is of prime importance to keepthepower used to produce a disturbing signal. as low .as possible. This isespecially true in long distance transmission, where high power mustnecessarily be used both for the de sired signal and the superimposedmasking signal] As pointed out above, since the disturbing noises areespecially efiective in masking the signals and they are onlytransmitted during signaling intervals, the energy requiredlto producethem is considerably less than in the systems in which noise currentsare continuously transmitted. Hence, under similar conditions, theamount of power required to transmit a signal to a distant station isconsiderably less than in systems heretofore known.

Although the invention has been described as applied to a radiotelephone sys tem, it is to be understood that by continuously actuatingthe microphone to produce amodulating current, or substituting asuitable modulating. current source therefor, and using a key to controlthe current supplied to both the signal and distortion producingmodulators in accordance with any code, this invention may be applied tothe transmission of telegraph signals.

What is claimed is:

1. In a carrier signaling system comprising means for producing acarrier wave modulated in accordance with signaling currents, means forrendering one of said side bands incapable of intelligible reception, byWaves derived from the signal source, and means for transmitting onlythe side band components of said wave.

2. In a carrier signaling system comprising means for producing acarrier wave modulated in accordance with variable frequency signalingcurrents, means for masking one of said side bands by a superim posedWave derived from the signal source, and means for transmitting the sideband components of said wave while suppressing the unmodulated carriercomponent.

3. In a carrier signaling system comprising a source of speech waves anda source of carrier waves, a. modulator for-combin ing said waves toproduce modulated components of said carrier wave while suppressing theunmodulated component, and means for masking one of said components by asuperimposed wave derived from the original speech waves source.

4. In a carrier signaling system including a source of signaling Wavesand a source of carrier waves, a balanced modulator "for combining saidwaves'to produce the side band components while suppressing theunmodulated component of said carrier wave, and means for masking one ofsaid side bands by a superimposed wave derivedfrom said signalingsource.

5. In a carrier signaling system including a source of signalingcurrents and a source of carrier waves, a balanced modulator forcombining said waves to produce side band components while suppressingthe unmodulated component of said carrier wave, and means for maskingone of said side band components by a wave modulated by currents fromsaid signaling source.

6. In a carrier signaling system including a source of signalingcurrents and a source of carrier waves, a balanced modulator forcombining said waves to produce side band components while suppressingthe unmodu- A lated component of said carrier wave, and

means for masking one of said side band' components by a wave modulatedby a demeans for masking one of said side bands comprising means forproducing a carrier wave modulated by current supplied from said signalstoring device and means for superimposing a portion of one of said lastmentioned side bands upon the side band produced by said first mentionedmodulator, and means supplying said superposed side bands to atransmission circuit.

8. In a carrier signaling system including a source of signaling currentand a source supplying a carrier wave of varying frequency, a balancedmodulator for combining said Wave and current to produce side band comonents while suppressing the unmodulate component of said carrier wave,a filter adapted to suppress a portion of one of said bands, atelegraphone, means for supplying signal current thereto, a secondmodulator for combining a carrier wave and current.

supplied by said telegraphone to produce side band components, a filteradapted to press a portion only of one of said last mentioned sidebands, means for combining the transmitted portion of said lastmentioned side band with the transmitted portion of said first mentionedside bands and means for supplying said combined side bands to atransmission circuit.

9. A method of carrier wave transmission which comprises combining acarrier wave and a signal wave to produce a modulated wave comprisingside band components, maskin one of said side bands by a superimposesignal modulated wave, and transmitting the superposed waves.

10. A method of carrier transmission which comprises combining a signalwave and a carrier wave to produce a modulated carrier wave consistingsolely of side band components, masking the components corresponding toone side band by superimposing thereupon a wave-modulated by delayedcurrent derived from the signal wave and transmitting the superposedwaves.

11. A method of carrier transmission which comprises combining a signalwere and a carrier wave to produce a modulated carrier wave consistingsolely of side band components, masking one of said side bands bysuperimposing thereupon a side band produced by modulating a wave bydelayed current derived from the signal wave and trans mitting saidsuperposed waves.

12. A method of secret carrier transmission which comprises combining aplurality.

sion which comprises combining signal'currentand a current derivedtherefrom with a plurality of carrier waves toproduce separate sets ofside band components, masking at least a part of one of the side bandcomponents of one of said sets by superimposing thereupon components ofthe other set, whereby one of the side band components of one of saidsets comprises a pure reproduction of the signal currents 14. The methodof renderin a transmitted signal diflicult of intelligi le receptionwhich comprises impressing the si nal elements upon a transmissionchannel, causing the impression of the signal elements to imand leavingthe channel free of disturbing elements when no signal elements are im-'pressed. I

15. The method which comprises generating a signal .wave having at leasttwo portions 'whose corresponding frequencies are equal,.generating acarrier Wave, combinin the carrier with one portion of the signa wave toproduce a modulated wave compris-' ing a pair of side bands, utilizinganother portion of the signal Wave to produce another pair of signalside bands which at least partially overlap one of the first mentionedside bands, super-posing the resultant pairs of side bands, andtransmitting the superposed waves.

16. The method recited in claim 15 in which the upper side band of thesecond mentioned pair of side bands substantially overlaps thelower sideband of the first mentioned pair of side bands.

In witness whereof, I hereunto subscribe my name this 23 day ofOctober-A. D., 1924.

RAYMOND A. HEISING;

